As an IRC, Slack, and Matrix user and netadmin, I will say that Slack and other nextgen chat services have a few advantages over IRC:

- automatic backlog resumption

- server stored pageable backlog

- continuous presence (you don't disappear from the channel when you leave, you're just marked as away)

- authentication built into the spec rather than implemented using a "services" layer

- general upgrades to what is allowed in the chat, such as long pastes, inline images, and file uploads

If you haven't tried Matrix yet (the best client is probably Riot at https://riot.im/ ), I encourage you to give it a try. It's essentially next generation IRC.

That sounds like having an irc client connected to say ZNC. It has all of the same features and has been around for years..

Sure, but a bouncer is another layer on top of your connection to the server, when architecturally it's much better to have the server manage that for you.

Why should end users care about the architecture? It's architecturally a hell of a lot better than a massive electron app that eats all of your RAM!

There are a million more embedded features in Slack than there are in IRC. Sure someone could spend a year trying to implement all of those plugins in their private IRC server and it be less functional and user friendly, but why would someone want to waste their time and money doing that?

IRC as a service. Allows users to pay a static amount each month and have a solid chat solution.